1. Field of the Invention
The present invention relates to a process for the plugging of a porous formation which may be encountered during the drilling of a well. The process entails plugging of the porous formation by means of a aqueous solution containing water-in-water pseudo-emulsion spheres. Preferably this aqueous solution which is a suspension of the spheres is prepared prior to injection into the well and then the aqueous solution suspension is injected into the well by suitable pump means. These particles penetrate the pore structure within a formation. Eventually, sufficient numbers of the spheres will accumulate within the pores, blocking further flow through the formation by both the pseudo-emulsion spheres and other aqueous solutions. The pseudo-emulsion system is formed by a process which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 100 cps; dissolving a neutralized sulfonated polymer in the solvent system to form a solution, a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps; and admixing or contacting said solution with about 5 to about 500 volume percent water, the water being immiscible with the organic liquid and the polar cosolvent and neutralized sulfonated polymer transferring from the organic liquid to the water phase, thereby causing the water phase to gel (i.e. thicken).
2. Description of the Prior Art
There are many applications for very viscous or gelled solutions of polymers in water which are quite diverse. There are also a number of physical and chemical techniques for preparing such systems. The present invention is concerned with a process for plugging a porous formation encountered during the drilling of a well, wherein the porous formation has water or salt water therein. If during the drilling of a well, a porous formation or water-bearing formation is encountered, a major problem which is faced is loss of material from the drilling fluid. If the loss of material from the drilling mud or dilution of a drilling mud with excess water becomes significant, the success of the drilling operation will be jeopardized. The instant invention provides a fluid loss additive which is capable of plugging the pores in the porous formation or water-bearing formation by providing an aqueous solution containing a large number of water-in-water pseudo-emulsion spheres which are capable of penetrating the pores structure within an underground formation. Preferably this aqueous solution which is a suspension of the spheres is prepared prior to injection into the well and then the aqueous solution suspension is injected into the well by suitable pump means. These particles will accumulate within the porous media, preventing further flow of both the pseudo-emulsion spheres and aqueous solution through the formation.
The instant invention differs from a number of applications, Ser. Nos. 223,482 now U.S. Pat. No. 4,361,658; 136,837 now U.S. Pat. No. 4,322,329; and 106,027 now U.S. Pat. No. 4,282,130, filed by Robert Lundberg et al, one of the instant inventors. These previously filed applications were directed to the gelling of the organic liquid by a water insoluble, neutralized sulfonated polymer whereas the instant invention is directed to the gelling (i.e., thickening) of an aqueous phase via a water-in-water pseudo-emulsion solution in order to plug a porous formation in a well. Quite unexpectedly, it has been discovered that when the concentration of the sulfonated polymer is maintained in a critical concentration range of 0.01 to 0.5 weight percent of the total volume of solvent, which is a mixture of nonpolar organic liquid and a polar cosolvent, upon the addition of water, a transfer of the polar solvent and water insoluble neutralized sulfonated polymer from the nonpolar organic liquid phase to the water phase occurs. The water insoluble neutralized sulfonated polymer causes the water phase to gel, wherein the neutralized sulfonated polymer is insoluble in the water phase. In the previously filed patent applications, substantial viscosification of the nonpolar organic liquid phase did not occur until the concentration of the neutralized sulfonated polymer was sufficiently high enough to permit chain entanglement of adjacent polymer molecules thereby completely filling the solvent space. The gelation of the aqueous phase of the instant invention does not occur by this previously described mechanism because the resultant concentration of water insoluble, neutralized sulfonated polymer is not sufficiently high enough to permit chain entanglement. The mechanism of gelatin of the aqueous phase, as defined in the instant invention, occurs by the formation of macroscopic, spherical polymer membranes or films dispersed throughout the aqueous fluid, wherein large volumes of the water of the aqueous liquid are encapsulated within a series of minute polymer bags (termed pseudo-emulsion spheres or particles).
The instant invention describes a process which permits (1) the preparation of polymer solutions of sulfonated polymers in organic liquid having reasonably low viscosities (i.e., less than about 2,000 cps); and (2) the preparation of a large number of pseudo-emulsion spheres within an aqueous fluid from such solutions by a process of contacting and agitating water with the polymer solution; and (3) the plugging of the pores of a porous formation in a well by the means of the formed aqueous pseudo-emulsion sphere system. These operations are achieved by the use of the appropriate concentration; 0.01 to 0.5 weight percent of water insoluble, neutralized sulfonated polymers, having low concentrations of ionic groups present, prefereably metal sulfonate groups. Such polymers are described in detail in a number of U.S. Patents (U.S. Pat. Nos. 3,836,511; 3,870,841; 3,847,854; 3,642,728; and 3,921,021) which are herein incorporated by reference. These polymers possess unusual solution characteristics some of which are described in U.S. Pat. No. 3,931,021. Specifically, these polymers, such as lightly sulfonated polystyrene, containing about 2 mole percent sodium sulfonate pendant to the aromatic groups, are typically not soluble in solvents commonly employed for polystyrene itself. However, the incorporation of modest levels of polar cosolvents permit the rapid dissolution of such ionic polymers to form homogeneous solutions of moderate viscosity.
In the instant process, the role of the polar cosolvent pertains to the following observation of solvating the ionic groups while the main body of the solvent interacts with the polymer backbone. For example, xylene is an excellent solvent for the polystyrene backbone and when combined with 5 percent methanol readily and rapidly, will dissolve the previous example of lightly sulfonated polystyrene.
The discovery of the instant invention is the ability of a large number of pseudo-emulsion spheres to penetrate a porous formation, preventing the loss of material from a drilling fluid. Preferably this aqueous solution which is a suspension of the spheres is prepared prior to injection into the well and then the aqueous solution suspension is injected into the well by suitable pump means. In addition, these spheres are capable of totally inhibiting flow of unwanted aqueous solutions into the drilling fluids. Even more remarkable is that the phenomena occurs via wholly hydrocarbon soluble sulfonated polymers at quite low polymer levels. The pseudo-emulsion system is formed by a process which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 100 cps; dissolving a neutralized sulfonated polymer in the solvent system to form a solution, a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps; and admixing or contacting said solution with about 5 to about 500 volume percent water, the water being immiscible with the organic liquid and the polar cosolvent and neutralized sulfonated polymer transferring from the organic liquid to the water phase, thereby causing the water phase to gel (i.e., thicken).